A galvanic cell is constructed using Zn|Zn²⁺ and Cu|Cu²⁺ half-cells. If the concentration of Zn²⁺ is increased from 1 M to 10 M at 25°C, how does this affect the cell potential? (E°cell = 1.1 V)
ADecreases by 0.0296 V
BIncreases by 0.0296 V
CIncreases by 0.059 V
DRemains unchanged
Correct Answer:
A. Decreases by 0.0296 V
EXPLANATION
Using Nernst equation: Ecell = E°cell - (0.059/n)log(Q). Increasing [Zn²⁺] increases Q, making the log term positive, which decreases Ecell. ΔE = -(0.059/2)log(10) = -0.0295 ≈ -0.0296 V.
During the electrolysis of molten NaCl using inert electrodes, if 2.3 g of Na is deposited at the cathode, what volume of Cl₂ gas (at STP) will be released at the anode?
A2.24 L
B1.12 L
C4.48 L
D0.56 L
Correct Answer:
B. 1.12 L
EXPLANATION
At cathode: Na⁺ + e⁻ → Na; moles of Na = 2.3/23 = 0.1 mol. At anode: 2Cl⁻ → Cl₂ + 2e⁻; for 0.1 mol Na, electrons = 0.1 mol, so Cl₂ moles = 0.1/2 = 0.05 mol. Volume at STP = 0.05 × 22.4 = 1.12 L.
For the reaction: Fe³⁺ + e⁻ → Fe²⁺ (E° = +0.77 V) and Cl₂ + 2e⁻ → 2Cl⁻ (E° = +1.36 V), which is the strongest oxidizing agent?
AFe³⁺
BFe²⁺
CCl₂
DCl⁻
Correct Answer:
C. Cl₂
EXPLANATION
The species with highest reduction potential (+1.36 V) is Cl₂, making it the strongest oxidizing agent. Higher E° values indicate greater tendency to accept electrons.
The cell potential of a galvanic cell decreases during operation because:
AThe concentration of reactants increases
BThe concentration of products increases
CTemperature continuously increases
DThe electrodes dissolve completely
Correct Answer:
B. The concentration of products increases
EXPLANATION
As the reaction proceeds, product concentrations increase while reactant concentrations decrease, reducing the driving force according to Nernst equation: E = E° - (0.059/n)log(Q).
A current of 5 A is passed through an electrolytic cell for 1930 seconds. Calculate the number of moles of electrons transferred. (Faraday constant = 96500 C/mol)
A0.1 mol
B0.5 mol
C1.0 mol
D2.0 mol
Correct Answer:
A. 0.1 mol
EXPLANATION
Charge = I × t = 5 × 1930 = 9650 C. Moles of e⁻ = 9650/96500 = 0.1 mol.